1. Field of the Invention
The invention relates to optical modulators in general and particularly to an electroabsorption modulator that employs Fermi level tuning.
2. Description of Related Art
Modulators are essential components of optical systems, enabling the conversion of a radio frequency signal into an intensity modulation on an optical signal. This can be used to encode a digital signal as a series of intensity pulses. In communications systems, the optical signals used are typically near 1550 nm in free space wavelength, but other wavelengths are possible. For example, commercial fiber optic-based telecommunication systems use signals in the vicinity of 1310 nm, 1490 nm and 1550 nm. In coarse wavelength division multiplexing (CWDM), a channel spacing grid using the wavelengths from 1270 nm through 1610 nm (revised to 1271 nm to 1611 nm) as center wavelengths with a channel spacing of 20 nm is an agreed ITU standard. Dense wavelength division multiplexing (DWDM) is another system used for standardized optical fiber-based telecommunication. In standard commercial systems, optical signals are converted to electrical signals for modulation, and are then converted back to optical signals for transmission.
One approach to building a modulator is to utilize a material that changes its absorption coefficient for optical radiation in response to an applied voltage. A typical means of achieving this is the Franz-Keldysh effect, which has recently been used with Ge—Si to build integrated electroabsorption modulators in a silicon platform.
There is a need for optical modulators that can modulate optical waves at extremely high speed, with low consumption of energy, and without requiring conversion of optical signals to electrical signals for modulation.